add re-emit note

Author: reaganjlee

src/_pytest/recwarn.py

@@ -150,6 +150,11 @@ def warns(  # noqa: F811
     This could be achieved in the same way as with exceptions, see
     :ref:`parametrizing_conditional_raising` for an example.
 
+    .. note::
+        By default, the function will re-emit all warnings that are not of the expected class.
+        By using the ``match`` keyword argument, all other un-matched warnings will be re-emitted.
+
+
     """
     __tracebackhide__ = True
     if not args: